The objective of this study is to assess central dopaminergic function in major depressive disorder (MDD). PET measures of [11C]-raclopride uptake will be acquired at baseline, after amphetamine (AMPH)-induced dopamine (DA) release and following a-methyl-para-tyrosine (aMPT) induced DA depletion in control and depressed samples. The 11C-raclopride uptake in these conditions will provide measures of the baseline dopamine D2/D3 receptor binding, the baseline occupancy of these receptors by endogenous DA and the amount of DA released following AMPH administration in each subject sample. These measures will be compared between depressives and controls to test the hypothesis that MDD is associated with a reduction in ventral striatal DA concentrations.